What is it?
Graves’ disease is the most common cause of an overactive thyroid gland (hyperthyroidism). It is caused by an antibody that acts like thyroid-stimulating hormone (TSH) and causes the thyroid gland to produce excess thyroid hormones (thyroxine (T4) and tri-idothyronine (T3)). This antibody has been given a variety of names and abbreviations including: TSH-receptor antibodies (TRAbs or TSH-Rabs), Thyroid Stimulating Immunoglobulins (TSI), Thyroid Binding Inhibiting Immunoglobulins (TBII) and Long Acting Thyroid Stimulator (LATS).
Those most likely to have Graves' disease are women over 20 years of age. Those with the disease may have protruding eyes, weight loss, increased appetite, nervousness and may have an increased heart rate and an enlarged thyroid gland (goitre) seen in the neck.
In addition to thyroid function tests (TSH, FT4, FT3), additional tests that can help in the diagnosis include:
- Radioactive iodine uptake. A capsule or “cocktail” containing a measured amount of radioactive iodine is swallowed. This is a perfectly safe procedure. Iodine is part of the thyroid hormones and is therefore taken up by the thyroid gland and more will accumulate in the gland if the gland is overactive, as occurs in Graves’ disease. A probe which measures radioactivity, is placed over the thyroid and the amount of radioactivity detected is compared to the amount that was given. Often a radioactive substance called Technecium-99 pertechnetate is used as an alternative to radioactive iodine; it behaves like radioactive iodine but it is more convenient to use and delivers a lower radiation dose to the patient.
- TSH Receptor Antibodies. In most patients with Graves’ disease the diagnosis can be made by the doctor following clinical examination together with the results of thyroid function tests and a thyroid scan. Measurement of these antibodies is therefore not always required. The measurement of TRAbs is useful when the cause of an overactive thyroid gland is unclear or in pregnancy when hyperthyroidism is suspected. Early in a normal pregnancy human chorionic gonoadotrophin (hCG) levels are high and some women have a brief period of mild hyperthyroidism due to the stimulating, TSH-like activity, of HCG but this is often not recognised by the mother. This brief period of mild hyperthyroidism is not harmful to the mother or her unborn baby. However, in pregnant patients with Graves’ disease the TRAbs antibodies may cross the placenta, over-stimulate the foetal thyroid gland, which may lead to miscarriage or poor growth of the baby. Since anti-thyroid drugs also cross the placenta, they treat both the maternal and foetal hyperthyroidism and it is essential to identify those pregnant women who have hyperthyroidism due to Graves’ disease. A high concentration of TRAbs towards the end of pregnancy can indicate thyroid disease (thyrotoxicosis) in the baby. Antibodies may also be present in patients who do not have thyroid disease or who have underactive thyroid glands (hypothyroidism) following treatment of Graves’ disease.
The measurement of TRAbs is helpful a) to identify Graves’ disease in pregnant women with hyperthyroidism, and b) in pregnant women who have a past history of Graves disease.
- Anti-thyroid peroxidase antibody. This autoantibody is found in most people with Graves’ disease, as well as in Hashimoto’s thyroiditis
Treatment is designed to reduce the amount of thyroid hormones produced by the thyroid gland. Beta-blockers, such as propranolol, may relieve rapid heart rate, sweating, and anxiety caused by increased activity. Drugs that reduce thyroid hormone production (antithyroid drugs) are often given initially. A large dose of radioactive iodine may then be given to try to destroy most of the thyroid gland, eliminating the symptoms of hyperthyroidism. Sometimes surgery to remove most of the thyroid gland is used. Usually the protrusion of the eyes decrease as the hormone concentrations are lowered.